High Definition Television or HDTV is the main change to broadcasting and television since the introduction of colour. Flat screen lcd televisions and plasma televisions with a minimum screen resolution of 1280 pixels x 720 pixels are known as HD Ready and are able of displaying current HD broadcasts.



What makes a Television 'HD Ready' ?

For a tv to be HD ready and display a high definition signal it ought to possess a minimum screen resolution of 1280 x 720 pixels, where 720 is the amount of vertical lines. It should also be capable to receive a signal of the specification of 720p/50 or 1080i/25; the quantity of vertical lines is represented by the 720 and the 1080, Progessive or Interlaced signals are signified by the 'p' or 'i', and the number of frames per second is the 50 or 25. Connection for the hi def signal is by either DVI or HDMI and Component inputs.

Any TV that has a screen resolution of 1366 x pixels 768 pixels and is HD Ready will make use of internal scalers to convert a 1080i signal down to the 768 lines; if it receives a 720p signal the internal circuits will upscale the image to 768 lines. The means of converting down or up is completed by means of highly developed software to fill the screen.

If a HD Ready tv receives a full HD signal of resolution 1920 x pixels 1080 pixels the picture signal has to be interpolated or converted down to show the image. One to one mapping of the pixels is not achievable.

What is 'HD ready 1080P' ?

A television that has the 'HD ready 1080P' label is able to show a full 1080p signal since it has enough pixels for one to one pixel mapping. This can be done with out Interpolation. The resolution of a 1080p flat screen television is 1920 x 1080 pixels or 1080P. The 1080 signifies the vertical resolution and the P is progressive scan. This is the maximum resolution offered in the United Kingdom on high definition tvs so that's why the term 'full'. TVs with this resolution are capable of displaying 1080p and 1080i signals without any distortion and with exact pixel for pixel mapping. They must also be equipped with DVI or HDMI inputs for 1080P signals at either 24 or 50 frames per second.

As soon as a 1080p HD tv receives s 720p input it will upscale (or oversample) the signal to the resolution of the 1080p HDTV widescreen using complicated internal software algorithms.

What is a Full HD Televisions ?

Before the HD ready 1080P specification was established some flat screen TVs were described as Full HD. These sets may not be compatible with the HD ready 1080P benchmark and may not display some inputs.

Interlaced Picture or Progressive Picture ?

Interlaced picture have two fields that are alternated to create a frame where every other line is shown on each frame. Thus the odd lines are on one field and the even lines are on the other field. When the two fields containing the odd and even lines are displayed one after the other for each frame at twice the frame rate this is known as Interlacing.

One of the benefits of Interlacing is that when footage is shot of a moving picture each of the fields of a frame are taken at separate times making motion that appears more fluid. Picture Interlacing is a system that was originally used to improve the image quality of a signal on CRT tvs without using extra signal bandwidth.

In the UK PAL tvs operates at 25 frames a second with 50 fields a second. A broadcasted signal that is Interlaced requires half the signal bandwidth of a Progressive signal. A progressive signal has a scan rate of 50 full frames per second in contrast with an interlaced signal which has half the frame speed.

Interlaced pictures on recordings made for television or with a video camera aren't able to be displayed on normal definition LCD tvs and Plasma tvs. This is because the picture isn't created with an electron scan like tube televisions so LCD televisions and Plama tvs don't benefit from the interlaced picture signal. Flat panel widescreen televisions have internal processing to make a progressive scanned picture from a interlaced picture - i.e. Deinterlacing.

The advantagess of progressive scanning

This is a method to show, transmit, and store a moving picture. Each frame has all of the lines rather than even lines or odd lines as with an Interlaced signal and they are shown in sequence.

The vertical resolution when the frame rate is the same is greater for a progressive image than it is for an interlaced picture and the image is free of interlace artifacts, blurring, and a good deal lower eye strain. With a progressive picture it can be scaled to a higher resolution than an interlaced image giving a higher quality image. This is due to the deinterlacing that is required on an interlaced image preceding any scaling resulting in combing artifacts that are evident.

720p/50 and 1080i/25 - What is the difference ?

On still images a 1080i/25 (1920 x pixels 1080 pixels) produces a slightly higher horizontal picture resolution than a 720p/50 (1280 x pixels 720 pixels) picture. Moving pictures on an interlaced picture have a lower subjective line resolution because of line twitter or artifacts caused by the fields being somewhat dissimilar that create a frame. Broadcasters have a tendency to opt for 1080i/25 over 720p/50 because it requires less bandwidth, but both systems are used for HD television broadcasts.

A progressively scanned 720p will generate smoother image movement than a 1080i interlaced signal, particularly on slow motion. With decent quality internal processing a 1080i seems to produce a better picture than a 720 signal. The best operating mode will depend on whether the screen is being used more with still images than moving images, and on the quality of the internal processing.

When a HD Ready television receives a 1080p/50 signal it can alter the image into a 1080i/25 picture much easier than a full HDTV can convert a 1080i signal into 1080p.

The benefits of a 1080p/24 signal.

Since the films that are shown in cinemas are created at 24 frames per second a signal is in its uncorrupted form at this frame rate. Films are available on Blueray disc at 24 frames per second with the purpose of givingthe ultimate picture quality when displayed on widescreen full HD televisions. When a full hd television receives a 1080p/24 signal it creates supplementary middle frames, which are inserted between the original ones to increase the frame rate to 48 or 72 frames per second giving more fluid motion.

HDTV Sources

HDTV broadcasts are currently at 720p/50 or 1080i/25 and are available on SKY Digital HD, Freesat, BT Vision, and Virgin media Cable. All of these necessitate a HD Ready TV. At present Full HD 1080P signals are only obtainable on Blue-Ray Disc, Playstation 3 and by download films on the web. The Xbox 360 games machine operates at 720p.

The conclusion

High definition television delivers an enhanced subjective picture quality that makes the reason for HD compelling. If you have possession of, or plan to own, a Playstation 3, a Blueray player, or download full HD films from the internet then a Full HD 1080p tv is the best option. If not a HD Ready television will be suitable. At the same time as these recommendations cover today's available options they don't allow for the likelihood of yet to come broadcasts in Full 1080p HD. If you want to be absolutely sure that you protect your purchase against this scenario then buy a Full 1080p HD flat panel TV.